Process for the oxidative coupling of hydrocarbons

ABSTRACT

A method for the oxidative coupling of hydrocarbons, such as the oxidative coupling of methane to toluene, includes providing an oxidative catalyst inside a reactor, and carrying out the oxidative coupling reaction under a set of reaction conditions. The oxidative catalyst includes (A) at least one element selected from the group consisting of the Lanthanoid group, Mg, Ca, and the elements of Group 4 of the periodic table (Ti, Zr, and Hf); (B) at least one element selected from the group consisting of the Group 1 elements of Li, Na, K, Rb, Cs, and the elements of Group 3 (including La and Ac) and Groups 5-15 of the periodic table; (C) at least one element selected from the group consisting of the Group 1 elements of Li, Na, K, Rb, Cs, and the elements Ca, Sr, and Ba; and (D) oxygen.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. application Ser. No.14/072,971, filed on Nov. 6, 2013, which is a Continuation of U.S.application Ser. No. 13/867,295, filed on Apr. 22, 2013, now issues asU.S. Pat. No. 8,729,328, which is a Divisional of U.S. application Ser.No. 12/494,138, filed on Jun. 29, 2009, now issued as U.S. Pat. No.8,450,546.

The present invention is related to co-pending applications titled:Catalysts For Oxidative Coupling Of Hydrocarbons; and Process For TheOxidative Coupling Of Methane, both filed by Fina Technology, Inc. onthe same date as the present application.

FIELD

The present invention generally relates to the oxidative coupling ofhydrocarbons.

BACKGROUND

Polystyrene is a plastic used in many applications. The plastic can beextruded, injection molded, or blow molded to make objects like plasticcups and utensils, and casings for CDs. Polystyrene can also be formedwith a rubber such as polybutadiene to make high impact polystyrene, orHIPS, which is more resistant to impact than normal polystyrene. HIPScan be used in toys, casings for appliances, and containers for food andmedical supplies. One of the most recognizable forms of polystyrene isits foamed form, which can be used in packing materials and can bemolded into containers, plates, cups and other shapes.

The monomer styrene is commonly produced via the dehydrogenation ofethylbenzene. This reaction can have several drawbacks, one being theformation of side products, such as benzene, toluene, and unreactedethylbenzene. Another drawback is that ethylbenzene and styrene havesimilar boiling points, which can make their separation difficult.

Ethylbenzene, in turn, is generally produced via the alkylation ofbenzene with ethylene. The reaction can create several side products,such as polyalkylated benzene. One significant drawback to this reactionis the relatively expensive reactants that are required. Both ethyleneand benzene can be obtained from refined petroleum. Ethylene is obtainedpredominantly from the thermal cracking of hydrocarbons, such as ethane,propane, butane, or naphtha, and generally goes through several cyclesof distillation to obtain a certain purity level. Ethylene from thesesources can include a variety of undesired products, including diolefinsand acetylene, which can be costly to separate from the ethylene.Thermal cracking and separation technologies for the production ofrelatively pure ethylene can result in significant production costs.

The costs associated with the production of polystyrene can beconsidered significant, when such production relies on the alkylation ofbenzene with ethylene and the dehydrogenation of ethylbenzene forobtaining the monomer styrene. It would be desirable to have alternatemethods for the production of ethylbenzene and styrene that is moreeconomical.

SUMMARY

Embodiments of the present invention generally include a method for theoxidative coupling of hydrocarbons, such as the oxidative coupling ofmethane to toluene. The method can include the steps of preparingoxidative catalysts and running the oxidative coupling reaction insidethe reactor over the oxidative catalyst, according to a set of reactionconditions.

An embodiment of the present invention is the preparation and/or use ofa catalyst that includes (A) at least one element selected from thegroup consisting of the Lanthanoid group, Mg, Ca, and the elements ofGroup 4 of the periodic table (Ti, Zr, and Hf). The catalyst furtherincludes (B) at least one element selected from the group consisting ofthe Group 1 elements of Li, Na, K, Rb, Cs, and the elements of Group 3(including La and Ac) and Groups 5-15 of the periodic table and (C) atleast one element selected from the group consisting of the Group 1elements of Li, Na, K, Rb, Cs, and the elements Ca, Sr, and Ba; alongwith (D) oxygen. If an element from Group 1 of the periodic table isused in (B), it cannot be used in (C). The catalyst can then be dried,calcined, and meshed before being placed in a reactor. The catalyst canbe calcined by heating the catalyst to elevated temperatures, such asabove 750° C.

The element(s) selected from (A) can range from 40 to 90 wt % of thecatalyst. The element(s) selected from (B) can range from 0.01 to 40 wt% of the catalyst. The element(s) selected from (C) can range from 0.01to 40 wt % of the catalyst. The oxygen in (D) can range from 10 to 45 wt% of the catalyst.

The product distribution of the oxidative coupling reaction can bealtered by adjusting the temperature of the reactor. Adjusting thetemperature can also alter the exotherm produced by oxidative coupling.

An embodiment of the invention is a method for the oxidative coupling ofmethane to toluene that includes providing a hydrocarbon feedstreamincluding methane and toluene and providing an oxidative catalyst withina reactor. The catalyst includes (A) at least one element selected fromthe group consisting of the Lanthanoid group, Mg, Ca, and the elementsof Group 4 of the periodic table (Ti, Zr, and Hf) the elements from (A)ranging from 40 to 90 wt % of the catalyst; (B) at least one elementselected from the group consisting of the Group 1 elements of Li, Na, K,Rb, Cs, and the elements of Group 3 (including La and Ac) and Groups5-15 of the periodic table, the elements from (B) ranging from 0.01 to40 wt % of the catalyst; (C) at least one element selected from thegroup consisting of the Group 1 elements of Li, Na, K, Rb, Cs, and theelements Ca, Sr, and Ba, the elements from (C) ranging from 0.01 to 40wt % of the catalyst; and (D) oxygen ranging from 10 to 45 wt % of thecatalyst; wherein if an element from Group 1 of the periodic table isused in (B), it cannot be used in (C); wherein the catalyst is calcinedafter the elements are combined. The hydrocarbon feedstream and anoxygen source are fed to the reactor wherein oxidative coupling ofmethane to toluene occurs over the oxidative catalyst according to a setof reactions conditions. A product stream that includes styrene andethylbenzene is recovered from the reactor.

The temperature can be from 500° C. to 800° C., optionally from 550° C.to 700° C. The molar ratio of methane to oxygen can be from 1:1 to100:1, optionally from 4:1 to 80:1. The molar ratio of methane totoluene can be from 1:1 to 50:1, optionally from 8:1 to 30:1. Thecatalyst can be pretreated in the reactor before it is used for theoxidative coupling of hydrocarbons, the pretreatment consisting ofheating the reactor to above 750° C. under an air flow for at least 1hour.

The composition of the product hydrocarbons can be adjusted by adjustingthe temperature of the reaction. The composition can also be adjusted byadjusting the space velocity of the reaction.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a graph displaying data, including conversion and selectivity,of OMT trials conducted in Comparative Example A.

FIG. 2 is a chart showing the conversion of toluene over varioustemperatures, from the OMT trials conducted in Example C.

FIG. 3 is a chart showing the selectivity of various products obtainedfrom the OMT trials conducted in Example C.

FIG. 4 is a chart showing data, including conversion and selectivity, ofthe OMT trials conducted in Example D.

FIG. 5 is a chart showing data, including conversion and selectivity, ofthe OMT trials conducted in Example E.

DETAILED DESCRIPTION

The results of oxidative coupling reactions can be influenced by manyfactors, such as reaction conditions, source and contents of the feed,and reactor design. The catalyst used for the reaction can be one of themost important factors. The effectiveness of the reaction can bemeasured in terms of conversion, selectivity, and yield. Conversionrefers to the percentage of reactant (e.g. methane) that undergoes achemical reaction. Selectivity refers to the relative activity of acatalyst in reference to a particular compound in a mixture. Selectivityis quantified as the proportion of a particular product relative to allothers.

An embodiment of the present invention is a process for the oxidativemethylation of toluene (OMT), as well as the oxidative coupling of otherhydrocarbons, including the steps of providing a catalyst and runningthe reactor according to a set of reaction conditions. The process caninclude steps such as preparing an oxidative catalyst, pretreating theoxidative catalyst inside a reactor, and carrying out the oxidativecoupling reaction inside the reactor, according to a set of reactionconditions. Preparation and pretreatment of the catalyst and reactionconditions can influence the conversion, selectivity, and yield of OMTand other coupling reactions.

One aspect of the process of the present invention involves thepreparation of a catalyst for OCM. A catalyst of the present inventiongenerally includes a substrate, one or more metal promoters and oxygen.The catalyst can vary in terms of its activity, useful run life, andothers characteristics. This variation can be influenced by theselection of the substrate and the combination of metal promoterssupported by the substrate.

According to an embodiment, the catalyst of the present invention caninclude a substrate that ranges from 40 to 90 wt % of the catalyst, thesubstrate made of one or more of the elements of Set A consisting of:the Lanthanoid group (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Th,Yb, Lu), Mg, Ca, and the elements of Group 4 of the periodic table (Ti,Zr, and Hf). The substrate supports a first promoter that ranges from0.01 to 40 wt % of the catalyst chosen from one or more of the elementsof Set B consisting of: Li, Na, K, Rb, Cs, and the elements of Group 3(including La and Ac) and Groups 5-15 of the periodic table. Thesubstrate further supports a second promoter that ranges from 0.01 to 40wt % of the catalyst chosen from one or more of the elements of Set Cconsisting of: Li, Na, K, Rb, Cs, Ca, Sr, and Ba. If an element fromGroup 1 of the periodic table (Li, Na, K, Rb, Cs) is used as a catalyticelement from Set B it cannot be used as a catalytic element from Set C.The catalyst further includes Set D, which consists of oxygen, in arange of 10 to 45 wt %. All percentages are for the catalyst aftercalcination.

The catalyst contains at least one element from each of the Sets A, B,C, and D in the ranges given above. At least 90 wt % of the catalyst ismade of the elements of Sets A, B, C and oxygen in the final catalystcomposition after a calcination procedure. Optionally at least 95 wt %of the catalyst is made of the elements of Sets A, B, C and D in thefinal catalyst after a calcination procedure. Residual anions may bepresent in the final catalyst, e.g. nitrate, halide, sulfate andacetate. The catalyst can vary in terms of its activity, its basicity,its lifetime, and other characteristics. This variation can beinfluenced by the selection of the elements chosen from Sets A, B, C andD and their respective content in the catalyst.

The various elements that make up the catalyst can be derived from anysuitable source, such as in their elemental form, or in compounds orcoordination complexes of an organic or inorganic nature, such ascarbonates, oxides, hydroxides, nitrates, acetates, chlorides,phosphates, sulfides and sulfonates. The elements and/or compounds canbe prepared by any suitable method, known in the art, for thepreparation of such materials.

The term “substrate” is not meant to indicate that this component isnecessarily inactive, while the other metals and/or promoters are theactive species. On the contrary, the substrate can be an active part ofthe catalyst. The term “substrate” would merely imply that the substratemakes up a significant quantity, generally 40% or more by weight, of theentire catalyst. The promoters individually can range from 0.01% to 40%by weight of the catalyst, optionally from 0.01% to 10%. If more thanone promoters are combined, they together generally can range from 0.01%up to 50% by weight of the catalyst. The elements of the catalystcomposition can be provided from any suitable source, such as in itselemental form, as a salt, as a coordination compound, etc.

The addition of a support material to improve the catalyst physicalproperties is possible within the present invention. Binder material,extrusion aids or other additives can be added to the catalystcomposition or the final catalyst composition can be added to astructured material that provides a support structure. For example, thefinal catalyst composition can be supported by a structured materialcomprising an alumina or aluminate framework. The content of such abinder material, extrusion aids, structured material, or otheradditives, and their respective calcination products, will not be takeninto consideration within the stated percentage ranges of Sets A-Dstated herein. As an additional example a binder material, which cancontain elements that are contained within Sets A-D, can be added to thecatalyst composition. Upon calcination these elements can be altered,such as through oxidation which would increase the relative content ofoxygen within the final catalyst structure. The binder material elementsand the calcination products are not taken into consideration within thestated percentage ranges of Sets A-D stated herein. The combination ofthe catalyst of the present invention combined with additional elementssuch as a binder, extrusion aid, structured material, or otheradditives, and their respective calcination products, are includedwithin the scope of the invention.

In one aspect, the invention is a method for the preparation of anoxidative catalyst for OMT, or another oxidative coupling reaction. Inone embodiment, the catalyst can be prepared by combining a substratechosen from at least one element from Set A with at least one promoterelement chosen from Set B, at least one promoter element chosen from SetC, and oxygen from Set D. The present invention is not limited by themethod of catalyst preparation, and all suitable methods should beconsidered to fall within the scope herein. Particularly effectivetechniques are those utilized for the preparation of solid catalysts.Conventional methods include coprecipitation from an aqueous, an organicor a combination solution-dispersion, impregnation, dry mixing, wetmixing or the like, alone or in various combinations. In general, anymethod can be used which provides compositions of matter containing theprescribed components in effective amounts. According to an embodimentthe substrate is charged with promoter via an incipient wetnessimpregnation. Other impregnation techniques such as by soaking, porevolume impregnation, or percolation can optionally be used. Alternatemethods such as ion exchange, wash coat, precipitation, and gelformation can also be used. Various methods and procedures for catalystpreparation are listed in the technical report Manual of Methods andProcedures for Catalyst Characterization by J. Haber, J. H. Block and B.Dolmon, published in the International Union of Pure and AppliedChemistry, Volume 67, Nos 8/9, pp. 1257-1306, 1995, incorporated hereinin its entirety.

In an embodiment, the substrate can be a metal oxide of one or moreelements of Set A. One example of an oxide substrate useful for thepresent invention is magnesium oxide, MgO. The oxide substrate can beeither obtained commercially or produced in the lab. For instance, ametal oxide can be made by thermal decomposition of its correspondingsalt at elevated temperatures up to 750° C. The choice of precursor saltfrom which the oxide substrate is produced can have some effect on theperformance of the eventual catalyst.

When slurries, precipitates or the like are prepared, they willgenerally be dried, usually at a temperature sufficient to volatilizethe water or other carrier, such as about 100° C. to about 250° C. Inall cases, irrespective of how the components are combined andirrespective of the source of the components, the dried composition isgenerally calcined in the presence of a free oxygen-containing gas,usually at temperatures between about 300° C. and about 900° C. for from1 to about 24 hours. The calcination can be in a reducing or inertatmosphere or an oxygen-containing atmosphere.

Depending on the catalyst, a pretreatment of the catalyst may, or maynot, be necessary. In one embodiment the invention involves thepretreatment of an oxidative catalyst for OMT, or another oxidativecoupling reaction. The prepared catalyst can be ground, pressed andsieved and loaded into a reactor. The reactor can be any type known inthe art to make catalyst particles, such as a fixed bed, fluidized bed,or swing bed reactor. The reactor set-up can optionally include arecycle stream. Optionally an inert material, such as quartz chips, canbe used to support the catalyst bed and to place the catalyst within thebed. For the pretreatment, the reactor can be heated elevatedtemperatures, such as 800° C. to 900° C. with an air flow, such as 100mL/min, and held at these conditions for a length of time, such as 1 to3 hours. Then, the reactor can be cooled down to a temperature of aroundthe operating temperature of the reactor, for example 500° C. to 650°C., or optionally down to atmospheric or other desired temperature. Thereactor can be kept under an inert purge, such as under helium.

In another aspect, the invention involves reaction conditions for OMT,or another oxidative coupling reaction. Several parameters includingfeed composition, molar ratio of hydrocarbon reactant to oxygen,temperature, pressure, time on stream, preparation method, particlesize, porosity, surface area, contact time and others can influence theoutcome of the reaction. For almost every reaction condition, there canbe a range of values best suited to oxidative coupling. Measures aregenerally taken to increase conversion and selectivity.

Although contaminants that might significantly interfere with theoxidative coupling reaction should be avoided, the addition of tracequantities of a reaction modulator may be useful. Reaction modulatorscan be used for the control or alteration of conversion, selectivity, oractivity of a particular catalyst or in response to certain reactionconditions. Non-limiting examples of possible reaction modulatorsinclude chlorine, ethylene and carbon monoxide.

Inert diluents such as helium and nitrogen may be included in the feedto adjust the gas partial pressures. Optionally, CO₂ or water (steam)can be included in the feed stream as these components may havebeneficial properties, such as in the prevention of coke deposits. Thepressure for oxidative coupling reactions can generally range from 1psia to 200 psia or more. The reaction pressure is not a limiting factorregarding the present invention and any suitable condition is consideredto be within the scope of the invention.

The temperature for oxidative coupling reactions can generally rangefrom 500° C. to 800° C., optionally from 600° C. to 750° C. The reactiontemperature is not a limiting factor regarding the present invention andany suitable condition is considered to be within the scope of theinvention.

Any suitable space velocity can be considered to be within the scope ofthe invention. As used herein the space velocity shall be defined as:space velocity=[feed flow as vapor (cm³/h)]/[catalyst weight (g)]. Astandard reference temperature and pressure (72° F. and 14.7 psia) isused to convert a liquid under these conditions, such as toluene, to afeed vapor flow. For example: 0.076 cm³/min of liquid toluene isconverted into moles and then using 22.4 L/mol (as if it were an idealgas) it is converted into a vapor flow of 16 cm³/min. The space velocitycan generally range from 15,000 cm³ g⁻¹h⁻¹ to 100,000 cm³ g⁻¹h⁻¹,optionally from 20,000 cm³ g⁻¹h⁻¹ to 85,000 cm³ g⁻¹h⁻¹. This range is anindication of possible space velocities, such as for a fixed bedreactor. Of course altering the catalyst composition, the amount ofinert material, etc can alter the space velocity outside of this range.Also a change in the reactor from a fixed bed to an alternate design,such as a fluidized bed can also dramatically change the relative spacevelocity and can be outside of the stated range above. The spacevelocity ranges given are not limiting on the present invention and anysuitable condition is considered to be within the scope of theinvention.

In the case of OMT, the feed will include toluene along with methane andoxygen. The toluene can be vaporized and introduced to the reactoreither by passing the oxygen and methane gas mixture through a toluenevapor saturator right before the inlet of the reactor tube, or bysyringe-pumping the liquid toluene into the gas flow and vaporizing itin a preheated zone (250˜300° C.) before entering the reactor. Themethane to oxygen molar ratio can range from 1:1 to 100:1, optionallyfrom 4:1 to 80:1. The molar ratio of methane to toluene can be from 1:1to 50:1, optionally from 8:1 to 30:1. Temperature can be from 300° C. to900° C., optionally from 350° C. to 750° C.

Although methane and toluene are considered the main reactants of OMT,oxygen can be another important component of the feed. Oxygen is arequired component of the feed for oxidative coupling. Methane can beobtained from natural gas, or from organic sources, such as thedecomposition of waste through fermentation. Whatever the source,methane used in OMT should not contain contaminants that mightsignificantly interfere or give a detrimental effect on the oxidativecoupling reaction. The oxygen source can be any source suitable forproviding oxygen to the reaction zone such as pure oxygen,oxygen-enriched air, or air. The gas containing oxygen should notcontain any contaminants that might significantly interfere with theoxidative coupling reaction. Alternate sources of oxygen may also beused, such as nitrobenzene, nitrous oxide or other oxygen containingcompounds.

For the present invention, the methane to oxygen molar ratio can be from1:1 to 30:1, optionally from 4:1 to 10:1. Oxygen can be fedintermittently, alternating with the hydrocarbon stream or optionallycan be fed simultaneously into the reactor with the hydrocarbonreactants.

Products leaving the reactor can be monitored with gas chromatography,or by some other method. Products can be separated using distillation orsome other method.

The following examples are intended to give a better understanding ofthe present invention in its many embodiments, but are not intended tolimit the scope of the invention in any way.

Comparative Example A

An oxidative catalyst was prepared comprising a MgO substrate that waspromoted with Ba. The Ba/MgO catalyst was used in the oxidative couplingof methane and the oxidative methylation of toluene. The catalystincluded 5% Ba by weight and was prepared from barium nitrate (6.53 g)(Sigma Aldrich, 98.0%) and MgO (23.46 g) (Fisher, 99%) by incipientwetness impregnation methodology in aqueous solution. The mixture wasdried at 120° C. for 3 h and then calcined at 850° C. in air for 1 h.The catalyst was ground, pressed and sieved to 20-40 mesh size (420-841μm) and 0. 0.577 g of catalyst was loaded into a quartz reactor usingquartz wool plugs and quartz chips to hold the catalyst bed in place.For catalyst pretreatment, the reactor was heated to 850° C. under 100ml/min of air and held for 2 hours. The reactor was then cooled down to600° C. under helium to prepare for the OMT experiments.

For the OMT experiments four trials were conducted, at reactiontemperatures between 550° C. and 650° C. All reaction conditions otherthan temperature were held constant during the four trials. The oxygensource was air. The methane to oxygen molar ratio was 5:1. The methaneto toluene molar ratio was 15:1. The total flow of gasses was 500cm³/min (240 cm³/min air, 244 cm³/min methane, 0.076 cm³/min liquidtoluene), and the space velocity was 51,993 cm³ g⁻¹h⁻¹. Product sampleswere taken after twenty minutes of run time and analyzed for productdistribution. The results of the trials are shown in the table below.

TABLE 1 Results for OMT over Ba/MgO catalyst Reaction Temperature 550°C. 570° C. 600° C. 650° C. Toluene Conversion (mol %) 3.2 6.8 7.3 9.9Benzene Selectivity (%) 65.8 85.4 74.5 49.3 Ethylbenzene Selectivity (%)3.6 5.0 5.8 7.0 Total Xylene Selectivity (%) 2.9 2.0 2.2 2.5 StyreneSelectivity (%) 9.6 18.5 25.5 41.4 Benzaldehyde Selectivity (%) 29.5 1.20.6 0.3 Total Stilbene Selectivity (%) 0.2 0.3 0.4 0.3

The results are also shown in FIG. 1. FIG. 1 is a graphicalrepresentation of the data presented in Table 1. The x-axis showstemperature from 540° C. to 650° C. The y-axis on the left side of thegraph corresponds to percent conversion of toluene. As can be seen,toluene conversion increased from 3% to 10% as temperature increased.The y-axis on the right side of the graph corresponds to percentselectivity for all of the products of the reactions. The productsincluded benzene, ethylbenzene, xylene, styrene, benzaldehyde, andstilbene. Benzene was the product with the highest selectivity. However,its selectivity peaked at 570° C. and steadily decreased thereafter.Styrene, on the other hand, steadily increased with temperature. Becauseconversion and the selectivity of key products can vary withtemperature, it may be possible to adjust product selectivity based ontemperature. Benzene and styrene, for instance, can both be valuableproducts. The demands for these products may vary, and it can thus beuseful to be able to control which of the two is the predominant productof OMT by adjusting the temperature. Selectivity of the other productswas less variable. For benzaldehyde, the selectivity rapidly decreasedfrom 30% to less than 1% at 575° C. Ethylbenzene selectivity, the totalxylenes selectivity, and the stilbene selectivity remained low in allthe trial runs.

Comparative Example B

An oxidative catalyst was prepared comprising an oxide substrate, MgO,that was promoted with Li. The Li/MgO catalyst was used in the oxidativemethylation of toluene. The catalyst included 2.5% Li by weight and wasprepared from Lithium carbonate (13.69 g) salt (Sigma Aldrich, 98.0%)and MgO (16.304 g) (Fisher, 99%) by incipient wetness impregnationmethodology in aqueous solution. The mixture was dried at 120° C. for 3hours and then calcined at 850° C. in air for 1 hour. The catalyst wasground and sieved to 20-40 mesh size and 0.542 g of catalyst was loadedin a quartz reactor using quartz wool plugs and quartz chips to hold thecatalyst bed in place. As a form of catalyst pretreatment, the reactorwas heated to 850° C. under 100 ml/min of air and held for 2 hours. Thereactor was then cooled down to 600° C. under helium to prepare for theOMT experiments.

For the oxidative methylation of toluene, the reaction temperature was650° C., the oxygen source was air, the total flow of gasses was 335cm³/min (150 cm³/min air, 150 cm³/min methane, 0.167 cm³/min liquidtoluene), the methane to oxygen molar ratio was 5:1, and the methane totoluene molar ratio was 15:1. The reaction was performed twice, at twodifferent space velocities. For the first trial, the space velocity was37,085 cm³ g⁻¹h⁻¹. For the second trial, the space velocity was adjustedto 70,295 cm³ g⁻¹h⁻¹ by diluting the feed with nitrogen gas (150 cm³/minair, 150 cm³/min methane, 0.167 cm³/min liquid toluene, 300 cm³/minnitrogen). Space velocity is inversely related to residence time in thereactor, and modulation of space velocity influences the contact timebetween reactants and catalyst. At a higher space velocity, residencetime and contact time are lower, and more reactants pass over thecatalyst in a given period.

The results of the two OMT trials are shown in Table 2 below. Gas andliquid samples were analyzed for product distribution at twenty minutes.

TABLE 2 Results for OMT over Li/MgO catalyst Space Velocity (cm³g⁻¹h⁻¹)37,085 70,295 Methane Conversion (mol %) 1.3 — Acetylene Selectivity (%)0.000 0.000 CO₂ Selectivity (%) 18.0 13.0 Ethane Selectivity (%) 0.0 0.3Ethylene Selectivity (%) 0.0 0.0 CO Selectivity (%) 5.6 3.8 TolueneConversion (mol %) 4.3 3.7 Benzene Selectivity (%) 58.6 58.3Ethylbenzene Selectivity (%) 2.6 2.3 Styrene Selectivity (%) 9.9 10.4 C₈Selectivity (%) 15.0 16.0 Stilbene Selectivity (%) 2.6 8.1

At the higher space velocity, there was greater selectivity to styrene(10.4% as compared to 9.9%). For toluene, the conversion dropped from4.3% to 3.7%. The selectivity to benzene and ethylbenzene formation didnot change with increasing space velocity. However, stilbene selectivityincreased dramatically from 2.6 to 8.1 mol %.

Example C

An oxidative catalyst was prepared comprising a MgO substrate that waspromoted with Na, Cs, and Re. The Na/Cs/Re/MgO catalyst was used in theoxidative methylation of toluene. The catalyst included 5% Na by weight(3.811 g) of sodium chloride, 5% Cs by weight (2.199 g) of cesiumnitrate, and 0.01% Re by weight (0.5856 g) of rhenium chloride and MgO(23.4033 g) (Fisher, 99%) by incipient wetness impregnation methodologyin aqueous solution. The mixture was dried at 120° C. for 3 h and thencalcined at 850° C. in air for 1 h. The catalyst was ground and sievedto 20-40 mesh size (420-841 μm) and 0.597 g of catalyst was loaded intoa quartz reactor using quartz wool plugs and quartz chips to hold thecatalyst bed in place. For catalyst pretreatment, the reactor was heatedto 850° C. under 100 ml/min of air and held for 2 hours. The reactor wasthen cooled down to 600° C. under helium to prepare for the OMTexperiments.

Five OMT trials were conducted, at reaction temperatures between 550° C.and 750° C. In all trials, the oxygen source was air, the total flow ofgasses was 500 cm³/min (244 cm³/min methane, 240 cm³/min air, 0.076cm³/min liquid toluene), the methane to oxygen molar ratio was 5:1, themethane to toluene molar ratio was 15:1, and the space velocity was50,251 cm³ g⁻¹h⁻¹. Product samples were taken after the first twentyminutes of run time and analyzed for product distribution. The resultsof the trials are shown in the table below.

TABLE 3 Results for OMT over Na/Cs/Re/MgO Temperature 550° C. 600° C.650° C. 700° C. 750° C. Toluene Conversion (%) 1.7 1.9 3.3 12.1 39.9Benzene Selectivity (%) 56.1 74.1 57.9 33.3 25.1 Total XyleneSelectivity 3.6 3.3 3.4 2.9 1.9 (%) Stilbene Selectivity (%) 3.3 0.9 0.50.2 0.2 Benzaldehyde Selectivity 30.6 12.6 6.3 2.0 2.0 (%) EthylbenzeneSelectivity 3.7 5.0 8.4 8.6 4.5 (%) Styrene Selectivity (%) 11.6 16.729.0 46.2 49.4

FIGS. 2 and 3 are graphical representations of the data shown in Table3. FIG. 2 shows the data for toluene conversion, with temperature on thex-axis and percent conversion on the y-axis. The conversion of tolueneincreased from 1.7% at 550° C. to 39.9% at 750° C. FIG. 3 shows the datafor selectivity. At temperatures from 550° C. to about 685° C., benzeneis the predominant product, with selectivity above 50%. At around 685°C., the selectivity for benzene and that of styrene intersect and above685° C., styrene is the predominant product. This approximatetemperature of 685° C. also marks a transition in the rate of formationof styrene. The selectivity of styrene rises significantly from 550° C.to 685° C. (from 11.6% to 46.2%) and rises relatively little (from 46.2%to 49.4%) above 685° C.

The selectivity of the other products decreased or remained low over thetemperatures explored. For instance, benzaldehyde selectivity decreasedfrom 30.6% at 550° C. to 2.0% at 750° C.

Styrene is most commonly the desired product of OMT. However, dependingon demand and process needs, other products can also be desired.Ethylbenzene, for instance, can be a desired product as the technologyis well established for its conversion to styrene via dehydrogenation.It is thus a useful feature of this process that product distributioncan be affected by modulation of reaction conditions such astemperature. Benzene was the product with the highest selectivity.However, its selectivity peaked at 600° C. and steadily decreasedthereafter. Styrene, on the other hand, steadily increased withtemperature. Because conversion and the selectivity of key products canvary with temperature, it may be possible to adjust product selectivitybased on temperature. Benzene and styrene, for instance, can both bevaluable products. The demands for these products may vary, and it canthus be useful to be able to control which of the two is the predominantproduct of OMT by adjusting the temperature.

Example D

An oxidative catalyst was prepared comprising an oxide substrate, MgO,that was promoted with Ca and La. The Ca/La/MgO catalyst was used in theoxidative coupling of methane to toluene. The catalyst included 5% Ca byweight from Calcium oxide (2.10 g) and 5% La by weight from lanthanumoxide (3.51 g) and was prepared from calcium oxide salt, La₂O₃ (SigmaAldrich, 98.0%) and MgO (24.38 g) (Fisher, 99%) by incipient wetnessimpregnation methodology in aqueous solution. The mixture was dried at120° C. for 3 hours and then calcined at 850° C. in air for 1 hour. Thecatalyst was ground and sieved to 20-40 mesh size and 0.661 g ofcatalyst was loaded in a quartz reactor using quartz wool plugs andquartz chips to hold the catalyst bed in place. As a form of catalystpretreatment, the reactor was heated to 850° C. under 100 ml/min of airand held for 2 hours. The reactor was then cooled down to 600° C. underhelium to prepare for the OMT experiments.

Four OMT trials were conducted over the Ca/La/MgO catalyst attemperatures of from 550° C. to 700° C. Reactions conditions other thantemperature were held constant. The oxygen source was air. The totalflow of gasses was 498 cm³/min (244 cm³/min methane, 240 cm³/min air,0.067 cm³/min liquid toluene). The methane to oxygen molar ratio was5:1. The methane to toluene molar ratio was 15:1. The space velocity was45,204 cm³g⁻¹h⁻¹. The products were analyzed after twenty minutes forproduct distribution. The table below shows results for the four OMTtrials.

TABLE 4 Results of OMT over Ca/La/MgO Temperature 550° C. 600° C. 650°C. 750° C. Toluene Conversion (%) 3.0 5.8 7.5 12.6 Benzene Selectivity(mol %) 60.6 40.4 39.5 28.1 Total Xylene Selectivity (mol %) 5.0 4.6 4.13.5 Stilbene Selectivity (mol %) 0.3 0.2 0.4 0.0 BenzaldehydeSelectivity (mol %) 1.4 0.1 0.0 0.0 Ethylbenzcne Selectivity (mol %) 5.95.7 5.2 4.5 Styrene Selectivity (mol %) 39.7 49.7 50.4 58.2

FIG. 4 is a graphical representation of the data shown in Table 4.Toluene conversion increased with increasing temperature, going fromabout 3% conversion at 550° C. to nearly 13% conversion at 700° C.Product distribution also varied with temperature. Styrene increased inselectivity from about 40% at 550° C. to nearly 60% at 700° C. All otherproducts had low selectivity and generally decreased in selectivity asthe temperature rose.

Example E

An oxidative catalyst was prepared comprising an oxide substrate, MgO,that was promoted with Sr and La. The Sr/La/MgO catalyst was used in theoxidative methylation of toluene. The catalyst included 5% Sr by weightfrom strontium nitrate (3.62 g) and 5% La by weight from lanthanum oxide(3.51 g) and was prepared from Sr(NO₃)₂ salt, La₂O₃ (Sigma Aldrich,98.0%) and MgO (22.85 g) (Fisher, 99%) by incipient wetness impregnationmethodology in aqueous solution. The mixture was dried at 120° C. for 3hours and then calcined at 850° C. in air for 1 hour. The catalyst wasground and sieved to 20-40 mesh size and 0.855 g of catalyst was loadedin a quartz reactor using quartz wool plugs and quartz chips to hold thecatalyst bed in place. As a form of catalyst pretreatment, the reactorwas heated to 850° C. under 100 ml/min of air and held for 2 hours. Thereactor was then cooled down to 600° C. under helium to prepare for theOMT experiments.

The Sr/La/MgO catalyst was used in four trials of OMT at temperaturesfrom 500° C. to 650° C. All reaction conditions other than temperaturewere held constant during these trials. The oxygen source was air. Thetotal flow of gasses was 498 cm³/min (244 cm³/min methane, 240 cm³/minair, 0.067 cm³/min liquid toluene). The methane to oxygen molar ratiowas 5:1. The methane to toluene molar ratio was 15:1. The space velocitywas 34,947 cm³g⁻¹h⁻¹. The products was sampled after 20 minutes andanalyzed for product distribution. The table below shows the results ofthe four OMT trials.

TABLE 5 Results of OMT over Sr/La/MgO catalyst Temperature 500° C. 550°C. 600° C. 650° C. Toluene Conversion (wt %) 0.4 1.1 6.1 15.8 BenzeneSelectivity (wt %) 30.4 51.0 40.4 16.2 Total Xylene Selectivity (wt %)15.8 6.7 3.9 2.5 Stilbene Selectivity (wt %) 1.3 0.2 0.2 0.3Benzaldehyde Selectivity (wt %) 21.2 5.7 0.1 0.0 EthylbenzeneSelectivity (wt %) 5.2 6.6 7.5 4.5 Styrene Selectivity (wt %) 4.5 22.243.0 42.1

FIG. 5 is a graphical representation of the data shown in Table 5. Thetoluene conversion increased with increasing temperature, from 0.4 wt %at 500° C. to 15.8 wt % at 650° C. Styrene selectivity also showed ageneral increase with increasing temperature, increasing from 4.5 wt %at 500° C. to 43.0 wt % at 600° C. The benzene selectivity showed aninitial increase in selectivity, with a peak of 51 wt % at 550° C. Attemperatures above 550° C., however, benzene selectivity decreased downto 16.2 wt % at 650° C. At about 595° C., the benzene and styreneselectivity intersect at about 42.0 wt %. This temperature also seems tomark a change in the rate of formation of styrene. Below 595° C.,styrene selectivity increased steadily with increasing temperature, butabove this temperature styrene selectivity changed very little. All theproducts except benzene and styrene showed a general decrease inselectivity with increasing temperature.

Styrene is most commonly the desired product of OMT. However, dependingon demand and process needs, other products can also be desired.Ethylbenzene, for instance, can be a desired product as the technologyis well established for its conversion to styrene via dehydrogenation.It is thus a useful feature of this process that product distributioncan be affected by modulation of reaction conditions such astemperature.

Figures are used herein to illustrate data, which are shown as datapoints on a graph. Lines connecting the data points are used to guidethe eye and assist in illustrating general trends of the data. The linesare not intended as a predictor of where additional data points wouldnecessarily fall, if they were available.

The term “C₂ selectivity” as used herein is the cumulative selectivityof acetylene, ethane, and ethylene.

The abbreviation of “OMT” as used herein refers to the oxidativemethylation of toluene to form new compounds. For instance, toluene cancouple with methane to form ethylbenzene and/or styrene.

Use of the term “optionally” with respect to any element of a claim isintended to mean that the subject element is required, or alternatively,is not required. Both alternatives are intended to be within the scopeof the claim. Use of broader terms such as comprises, includes, having,etc. should be understood to provide support for narrower terms such asconsisting of, consisting essentially of, comprised substantially of,etc.

As used herein the space velocity shall be defined as: spacevelocity=[feed flow as vapor (cm³/h)]/[catalyst weight (g)].

Depending on the context, all references herein to the “invention” mayin some cases refer to certain specific embodiments only. In other casesit may refer to subject matter recited in one or more, but notnecessarily all, of the claims. While the foregoing is directed toembodiments, versions and examples of the present invention, which areincluded to enable a person of ordinary skill in the art to make and usethe inventions when the information in this patent is combined withavailable information and technology, the inventions are not limited toonly these particular embodiments, versions and examples. Other andfurther embodiments, versions and examples of the invention may bedevised without departing from the basic scope thereof and the scopethereof is determined by the claims that follow.

What is claimed is:
 1. A method for the oxidative coupling of methane toa hydrocarbon other than methane comprising: providing a hydrocarbonfeedstream comprising methane and a hydrocarbon other than methane;providing an oxidative catalyst within a reactor, the catalystconsisting essentially of: (A) Mg element from 40 to 90 wt. % of thecatalyst; (B) La element from 0.01 to 40 wt. % of the catalyst; (C) Caelement from 0.01 to 40 wt. % of the catalyst; and (D) oxygen, whereinoxygen comprises from 10 to 45 wt. % of the catalyst; feeding thehydrocarbon feedstream and an oxygen source to the reactor; carrying outoxidative coupling of the methane to a hydrocarbon other than methaneover the oxidative catalyst according to an oxidative coupling; andrecovering product hydrocarbons comprising ethylbenzene and styrene. 2.The method of claim 1, wherein the hydrocarbon other than methanecomprises toluene.